Triboelectric spray guns may be used to spray fine powders in various applications including painting or specialized powder coating applications such as controlled, or supplementary pollination of plants. These sprayers use pressurized gas to expel particles which are electrostatically charged during the expulsion process due to their contact and friction with one or more surfaces within the gun. This xe2x80x9ctriboxe2x80x9d, or xe2x80x9cfrictionxe2x80x9d charging distinguishes these spray guns from other types of electrostatic spray guns which use electrodes to impart a charge on the powder particles during the spraying process.
In a typical manual configuration, a triboelectric spray gun with its accompanying components comprises a hand held sprayer which is attached by electrical wiring and tubing to a controller module and a source of material, such as powder, to be sprayed. Usually the gun is equipped with a trigger which activates an electrical switch and the switch, in turn, activates the controller module. The controller module controls the delivery of one or more airs to the gun which draw powder into the gun, accelerate the powder and expel it in an electrically charged state.
Although this arrangement may work well in some circumstances, it is inherently unsafe because the operator of such a system is constantly in contact with an electrical switch and the gun itself is connected to electrical wiring. This may pose a danger to the operator because electrical connections may result in shocks or sparks which can ignite the material being expelled from the sprayer. Further, operators working outside or in greenhouses or shade houses may be exposed to weather or misting or fogging systems, and would benefit from a system which included a spray gun and a controller module which were both isolated from electrical connections.
One alternative to an electrical switching device is a switching device which is controlled by air, such as by an air-solenoid. U.S. Pat. No. 5,615,832 describes an apparatus which uses both electrical and air solenoid type switches to control airs in a triboelectric gun. However, this apparatus includes a relatively complex arrangement of electrical circuits to regulate the airs. Therefore, this apparatus is still burdened with electrical connections and wiring which may lead to electrical shocks or sparks.
Another alternative is found in U.S. Pat. No. 3,740,612. This device includes a trigger which activates two air solenoid/valve type arrangements. However, the apparatus described in this patent is an electrostatic sprayer which necessarily includes high voltage wiring leading to an electrode which charges the powder as it is expelled from the gun. The result is that this device still poses a shock or sparking danger to its operator.
Further alternatives include those found in U.S. Pat. Nos. 5,850,976 and 6,003,779 which disclose sprayers with air valves that control the spraying operation. However, these devices include a system for fluidizing the powder in the reservoir and are not effective for spraying measured amounts of powder.
Thus, there is a need for a triboelectric sprayer which improves upon the art by allowing an operator to manually operate the gun without being exposed to high or low voltage shocks, sparks or the dangers related thereto. Further, there is a need for an inexpensive method for controlling a spray gun apparatus with no electrical connections. In addition, there is a need for a metering device which will operate with a fully air controlled gun and which can also be controlled without electrical connections. And further, there is a need for a device particularly suited for delivering small, measured quantities of electrically charged pollen, which is inexpensive, simple to operate and particularly suitable for outdoor use.
Accordingly, it is a principal object of the invention to provide a spraying system which improves upon the prior art by eliminating all electrical controls from a triboelectric spray gun and controller module so that they are suitable for outdoor use and other applications, while optionally adding a metering system which allows a measurable and repeatable amount of particles to be expelled from the sprayer.
In accordance with one preferred embodiment of the invention the apparatus comprises a means for controlling airs to a triboelectric spray gun with signals generated with compressed air.
In accordance with another preferred embodiment of the invention the apparatus comprises a metering device which delivers metered amounts of powder to a spray gun and which is controlled with compressed air.
In accordance with another preferred embodiment of the invention the apparatus comprises both the air controlling means and the metering device, the metering device being controlled by the same compressed air which controls the airs.